Checks if a list of values are being used in actual field values.
function _list_values_in_use($field, $values) {
if ($values) {
$query = new EntityFieldQuery();
$found = $query
->fieldCondition($field['field_name'], 'value', $values)
->range(0, 1)
->execute();
return !empty($found);
}
return FALSE;
}